Model 100 upgradeI've designed a new mainboard for the Tandy / RadioShack TRS-80 Model 100, one of the very first tablet computers. The machine turns thirty years old this year and, amazingly, many of them still function! My upgrade replaces the Model 100's 2.4 MHz 80C85 with the more modern 16 MHz AVR AT90USB1286 on a Teensy++ and adds new features like VT100 emulation and the potential to increase the storage from the original by a factor of one million.

Currently the only function implemented in the new firmware is a USB serial terminal. The real Model 100 had a text editor and a BASIC written by Bill Gates himself, in addition to a (non-VT100) serial monitor and an analog modem. Porting busybox vi to the AVR is doable now that there is a VT100 emulator, and using something like pForth for the interactive programming wouldn’t take much code space. It would be a very fun project to write a 300 baud software modem to drive the acoustic couplers, but where would you find a phone to use it with?

Adding MicroSD card support to store documents would expand the space available from the original 32 KB of battery-backed RAM to a more modern 32 GB. Plus the SD cards are non-volatile, so all of your work won’t be lost if the batteries die. Another option would be to add a Raspberry Pi into the case, using the Teensy to act as a serial console for it since the Pi lacks sufficient IO and 5V tolerance.

Perhaps these portable devices will have another thirty years of life left in them with a few minor upgrades…